Need assistance with conditional join in SQL

Question

Hi All -
I need to ask for help with this query:
Create table user_tab_col_test (table_name varchar2(30), column_name varchar2(30), data_type varchar2(30));
Insert into user_tab_col_test (table_name, column_name, data_type) values ('table1', 'column1', 'varchar2')
Insert into user_tab_col_test (table_name, column_name, data_type) values ('table1', 'column2', 'varchar2')
Insert into user_tab_col_test (table_name, column_name, data_type) values ('table1', 'column3', 'varchar2')
Insert into user_tab_col_test (table_name, column_name, data_type) values ('table1', 'column4', 'varchar2')
Insert into user_tab_col_test (table_name, column_name, data_type) values ('table2', 'column1', 'varchar2')
Insert into user_tab_col_test (table_name, column_name, data_type) values ('table2', 'column2', 'varchar2')
Insert into user_tab_col_test (table_name, column_name, data_type) values ('table2', 'column3', 'varchar2')
Insert into user_tab_col_test (table_name, column_name, data_type) values ('table2', 'column4', 'varchar2')
Commit;
Create table all_cons_columns_test (table_name varchar2(30), column_name varchar2(30), constraint_name varchar2(30))
Insert into all_cons_columns_test (table_name, column_name, constraint_name) values ('table1', 'column1', 'primary')
Insert into all_cons_columns_test (table_name, column_name, constraint_name) values ('table1', 'column1', 'secondary')
Commit;
This is my query and the current result:
Select u.table_name, u.column_name, c.constraint_name
From user_tab_col_test u
Left outer join all_cons_columns_test c
On ( u.table_name = c.table_name
AND U.COLUMN_NAME = C.COLUMN_NAME
AND C.CONSTRAINT_NAME IN ('primary'))
order by U.table_name, U.COLUMN_NAME;
TABLE_NAME COLUMN_NAME CONSTRAINT_NAME
table1 column1 primary
table1 column2
table1 column3
table2 column1
table2 column2
Three questions:
1) I only want to return results where table_name = 'table1'. I can't seem to get this to work.
2) Is my query proper and is this the best way to return my desired results? I.e. I want all columns from user_tab_col_test and I only want to display the constraint_name from all_cons_columns_test if the constraint_name = 'primary'.
3) Will the synatx be the same if I need to join a third table to all_cons_columns_test?
Any advice/suggestions are much appreciated -
john
Edited by: user703358 on Jan 11, 2013 8:57 PM
Edited by: user703358 on Jan 11, 2013 9:48 PM

Answer 1

Hi,
user703358 wrote:
... ALL_CONSTRAINTS_TEST joins to ALL_CONS_COLUMNS_TEST on TABLE_NAME and CONSTRAINT_NAME. If you adapt this to use the data dictionary views ALL_CONSTRAINTS and ALL_CONS_COLUMNS, then rememeber to join on the OWNER column, also.
Ultimately I want to use ALL_CONSTRAINTS_TEST.CONSTRAINT_TYPE = 'P' in my WHERE clause, instead of C.CONSTRAINT_NAME IN (primary), only because the constraint_type is a more definitive attribute than just the name of the constraint.
I tried something like the query below but I'm getting
ORA-00904: "U"."COLUMN_NAME": invalid identifier
00904. 00000 - "%s: invalid identifier"
*Cause:  
*Action:
Error at Line: 8 Column: 16Errors like that are caused by trying to mix old join syntax with ANSI join syntax in the same query.
SELECT    u.table_name
,       u.column_name
,       C.CONSTRAINT_NAME
FROM           USER_TAB_COL_TEST      U,
ALL_CONSTRAINTS_TEST ACAbove is an example of an old-style join: there is a comma between the table names, and the join conditions are included in the WHERE clause below.
LEFT OUTER JOIN  all_cons_columns_test  c
ON    u.table_name    = c.table_name
AND   U.COLUMN_NAME    = C.COLUMN_NAMEThis is an example of an ANSI-style join: the keyword JOIN appears between the table names, and the join conditions are right here, after the keyword ON.
WHERE      U.TABLE_NAME    = 'table1'
AND C.TABLE_NAME = AC.TABLE_NAME
AND C.CONSTRAINT_NAME = AC.CONSTRAINT_NAME
and AC.CONSTRAINT_TYPE = 'P'
ORDER BY  u.table_name
,           u.column_name
;While it is possible to use both join styles in the same query, it's a really bad idea. I suggest always using ANSI syntax, especially for outer joins, but whatever style you choose, use it consistently for all joins in the same query.
In this case, you want an inner join between tablec c and ac, so the ANSI syntax would be something like
FROM  u  LEFT OUTER JOIN c ON ... JOIN ac ON ...In this case, it's very important that the inner join between c and ac is done before the outer join with u. How can you make sure that happens? Well, if you have an arithmetic expression such as
12 * 5 - 1and you want to make sure the subtraction of 1 from 5 takes place before the multiplication by 12, what do you do? You can add parentheses:
12 * ( 5 - 1 )In ANSI join syntax, you can use parentheses the same way:
FROM  u  LEFT OUTER JOIN ( c ON ... JOIN ac ON ... )or, in full:
SELECT    u.table_name
,        u.column_name
,        c.constraint_name
,       ac.constraint_type
FROM             user_tab_col_test      u
LEFT OUTER JOIN  (
                         all_cons_columns_test  c
           JOIN  all_constraints_test   ac
                             ON   ac.table_name     = c.table_name
                      AND  ac.constraint_name     = c.constraint_name
                        ON    u.table_name       = c.table_name
               AND   u.column_name       = c.column_name
               AND   ac.constraint_type  = 'P'
WHERE       u.table_name     = 'table1'
ORDER BY  u.table_name
,            u.column_name
;Output:
TABLE_NAME COLUMN_NAME CONSTRAINT_NAME CONSTRAINT_TYPE
table1     column1     primary         P
table1     column2
table1     column3
table1     column4